Siamese cats often have a neurological oddity which routes some of the nerves from each eye to the same hemisphere of the brain, rather than crossing over as is normal in mammals. (Websearch "siamese strabismus" and "optic chiasm" for details. I found it fascinating to discover that something similar may happen in partial-albino big cats.)
Siamese compensate for this miswiring either by becoming cross-eyed (which used to be reqired for show cats; that was finally dropped, though the modern show siamese has its own you-gotta-be-kidding rules) or by rapidly flicking their eyes back and forth to "average out" the visual oddities.
Many 'meezers and part-meezers who don't show either of those symptoms normally will do so when tired. Mine used to do so. ("Cat, you're woggling again...")
If this is what's happening, it's "normal" in the sense of being genetic and harmless for a housecat, though it would be a handicap in the wild.
To make sure, do check with your vet, since concussion and the like can also disrupt vision and muscle control. But in this case it is probably harmless.
(Darned touch-screen typos...)